Dopamine release in the nucleus accumbens is important for reinforcement learning of cues associated with natural and drug related rewards. Cocaine enhances dopamine signals in the accumbens through multiple mechanisms including reduced uptake which results in larger dopamine signals, as well as increases in frequency of spontaneous dopamine release events. Cocaine's mechanism of action for enhancing spontaneous release frequency is currently unknown. Recent studies have underscored the importance of cholinergic signaling onto dopamine terminals. Most notably, optogenetic stimulation of cholinergic interneurons is sufficient for driving dopamine release. Furthermore, cocaine enhances cholinergic firing, and inhibition of cholinergic activity during cocaine exposure reduces cocaine reward in condition place preference paradigms. Together, these observations indicate that the cholinergic neurons play a major role in modulating the release of dopamine within the accumbens during cocaine exposure. In preliminary experiments, spontaneous dopamine release was observed using voltammetry in brain slices containing the nucleus accumbens. These spontaneous dopamine events were infrequent, small and increased in the presence of cocaine. Furthermore, cocaine-enhanced spontaneous dopamine release was reduced by nicotinic acetylcholine receptor blockade. The overall goal of the current proposal is to investigate the origin of spontaneous dopamine signals. The hypothesis is that these spontaneous signals are driven by the activity of the cholinergic interneurons that result in the release of acetylcholine that act on nicotinic receptors on local terminals from dopamine neurons. This hypothesis will be tested using a combination of voltammetry and electrophysiology techniques in a paired recording configuration in coronal striatum mouse brain slices. Together, these results will reveal several important mechanisms underlying the local regulation of dopamine release in the nucleus accumbens and striatum. Furthermore, these studies will provide information on cocaine's effects on cholinergic activity important for drug reward/reinforcement.